1. Field of the Invention
The present invention relates to a disk array apparatus having a disk array constituted by a plurality of disk drives, and a data update method in the disk array apparatus.
2. Description of the Related Art
Conventionally, a disk storage management method called a log-structured file system has been known. The log-structured file system is described in detail in, e.g., Mendel Rosenblum and John k. Ousterhout, “The Design and Implementation of a Log-Structured File System”, ACM Transaction on Computer Systems, February 1992. The log-structured file system described in this reference can be summarized as a method of writing a plurality of updated data altogether in contiguous areas which do not store valid data and are different from old areas, and invalidating the old areas where the valid data have been stored before updating.
U.S. Pat. No. 6,219,752 and No. 6,233,648 disclose a technique in which the log-structured file system is applied to a disk array apparatus (to be referred to as a prior art, hereinafter). In this prior art, when receiving an update (write) request from a host computer, contents in the storage area of old data to be updated are not normally rewritten, and the updated data is stored in a buffer first. When updated data with a predetermined quantity are stored in the buffer, these updated data are written in empty areas other than the area of the old data on the plurality of disk drives in bulk, that is, en bloc. Such a write method is called as a delay write method.
In the prior art described above, when the logical address designated by an access request from the host computer is to be translated into a physical address on the disk array, an address translation table is used. To construct this address translation table requires a logical address tag block. The logical address tag block contains logical addresses of a plurality of logical blocks which make up data to be written in bulk (data of one stripe), and a time stamp for representing a time order that these data are written.
In the prior art described above, the logical address tag block is treated as a part of data to be written in bulk (data of one stripe). Logical address tag blocks contained in these data cannot be obtained unless data for all stripes are loaded from the disk array. Therefore, when an address translation table is reconstructed by using logical address tag blocks in a case wherein, e.g., an abnormality occurs, the reconstruction process requires a very long period of time.
The logical address tag block in the above-described prior art is written midway along the plurality of physically contiguous data blocks on the disk array. Thus, when the plurality of physically contiguous data blocks are to be read out from the disk array, the logical address tag block present midway along the data blocks inhibits efficient data readout operation.